WASHINGTON (Reuters) - The U.S. pipeline safety office is struggling to inspect natural gas storage sites and uphold other standards on the facilities, according to a report released by the General Accountability Office on Friday

After a leak at California's Aliso Canyon underground storage plant spewed natural gas for months, Congress updated pipeline standards in a bill signed by former President Barack Obama last year.

The law required the Pipeline and Hazardous Materials Safety Administration, or PHMSA, an office of the Department of Transportation to set safety standards at the storage sites by June 2018. PHMSA issued an interim rule that took effect in early 2017, largely based on practices recommended by energy industry lobbying group the American Petroleum Institute.

But the GAO found inspections on the sites were lacking despite the interim rule. PHMSA currently "focuses on training and does not address other core program activities, such as conducting effective inspections," it said.

The non-partisan GAO works for Congress and investigates how the federal government spends taxpayer dollars.

The Aliso Canyon leak from a 60-year old well led to the temporary relocation of 8,000 families in 2015. Emissions of the greenhouse gas methane from the facility had a comparable effect on global warming that all the emissions of Costa Rica had during the same period, scientists say.

Representative Eddie Bernice Johnson, a Democrat from Texas who requested the GAO review, said she was concerned inspection lags combined with delays in complying with new safety standards could put public health and safety at risk. There are 415 gas storage sites across 31 states.

"We must ensure that this important energy resource is monitored, developed and overseen with safety in mind," Johnson said.

PHMSA did not immediately respond to a request for comment about the report. But the GAO said the Transportation Department concurred with its recommendations, including defining levels of performance and improving inspections.

Separately, Kevin McIntyre, the new chairman of the Federal Energy Regulatory Commission, said this week his agency would review policies on approvals of new natural gas pipelines. FERC has not updated the policies since 1999.

Some recent approvals of new pipelines, such as the Atlantic Coast Pipeline from West Virginia to North Carolina, have taken two years or more. Neil Chatterjee, a fellow Republican of McIntyre's on the FERC committee, said last month he hoped lengthy approvals would not become the new norm.